A methylene blue-based tri-mode “turn-on” molecular probe for detecting Hypochlorous acid in human serum

Hypochlorous acid (HClO), a key reactive oxygen species, oxidative stress induced by its abnormal levels is associated with various human diseases. This study develops a multi-mode (electrochemical, near-infrared fluorescence, colorimetric) detection system (MB-NB probe) for accurate serum HClO detection. The MB-NB probe uses methylene blue (MB) as the signal reporting unit (with electrochemical activity, characteristic color, and near-infrared fluorescence properties), and phenylboronic acid pinacol ester as the specific recognition site for HClO. When HClO interacts with the probe, the boronate ester group undergoes an oxidative deborylation reaction, which triggers the cleavage of the amide bond and the release of free MB, which synchronously induces three characteristic signal changes: in the electrochemical mode, the reduction peak current at −0.31 V increases linearly with the concentration of HClO (detection range: 2–80 μM; detection limit: 0.23 μM); in the colorimetric mode, the absorption peak at 665 nm is enhanced and the solution changes from colorless to blue; in the fluorescence mode, the near-infrared fluorescence intensity at 685 nm is significantly enhanced (linear range 10–100 μM). The tri-mode detection system provides a reliable tool for the accurate determination of HClO levels in serum, thus laying a technical foundation for in-depth exploration of the associations between changes in HClO content and the pathogenesis of various human diseases.